The present invention relates to a tube or a duct for transporting a motor vehicle fluid and in particular a coolant in an internal combustion engine, for example.
Currently known prior art comprises:
rubber (ethylene-propylene diene monomer or xe2x80x9cEPDMxe2x80x9d) tubes which may optionally be reinforced depending on the pressure levels and/or the temperatures of the fluids which flow therein;
metal tubes that are lined with and associated with rubber (EPDM) ducts enabling the movements and the vibrations generated by the engine to be absorbed; the rubber tubes are used in particular for making the connections to members such as the engine, the radiator, the expansion tank . . . . The drawback of those systems lies in the significant size of the pipework given the existence of the metal tubes, in the relatively high rigidity of the system, and in the problems of the metal tubes corroding despite the lining applied thereto;
single layer pipes made of rigid thermoplastic such as polyamide (in particular PA 66) filled with glass fiber; these pipes are very rigid and consequently have the drawback of transmitting vibration, and of giving off noise as a result of the vibration and also as a result of the flow of fluid passing therealong;
thermoplastic pipes having various rigid and flexible segments for absorbing vibration and movements generated by the engine; however, the flexible portions must be reinforced by a structure which limits both their radial expansion and their axial lengthening; the flexible portions are either made integrally with the rigid portions, or independently of said rigid portions and are assembled thereto by welding. The drawback of that technique essentially lies in its complexity and in the large number of manufacturing operations; and
multilayer pipes made of synthetic material that is either entirely thermoplastic, or thermoplastic only in part, in which case the thermoplastic portion forms the inner layer of the pipe; the drawback of such a pipe lies in it being difficult, if not impossible, to connect to current rigid endpieces (e.g. a spigot), thus making it necessary to use an intermediate connection piece.
To mitigate the drawbacks of the prior art, the invention proposes a tube structure for transporting a fluid flowing in motor vehicle engines, and in particular a coolant, which tube structure also satisfies particularly strict specifications, and does so under good economic production conditions. It is necessary for this type of tube to be manufactured in simple manner and therefore at low cost, for it to continue to have some rigidity enabling it, in particular, to retain the shapes imposed on it prior to its final assembly, for it to present very high performance with regard to permeability, and in particular, much higher performance than that of the rubber ducts used until now, and finally, for said multilayer structure to be capable of withstanding assembly forces of the force-fit type without the various layers making it up separating under the effect of said forces.
Thus to this end, the invention provides a tube for transporting a motor vehicle fluid such as a coolant, which tube comprises:
an inner layer made of vulcanized elastomer material;
an outer layer made of thermoplastic material that withstands the coolant chemically and that is impermeable thereto; and
an intermediate bonding layer made of a material that is compatible with the materials of the inner and outer layers.
In addition to satisfying the above-mentioned specifications, such a structure enables tubes to be made that are adapted to the mechanical performance that is required of them. Thus, the inner layer made of vulcanized elastomer material has a thickness that is adapted, for example, to the dimensions of the projection on the rigid endpieces onto which the tube is to be force fitted. In addition, the thickness of the outer layer made of thermoplastic is chosen as a function of the stiffness desired for the tube, which stiffness is compatible with the levels of movement and of vibration allowed when the tube is installed in the vehicle. The thickness of the intermediate layer itself lies in the range {fraction (1/10)}th to {fraction (3/10)}ths of a millimeter, said layer not having any mechanical function, but merely the function of interconnecting the two layers which surround it.
In an embodiment of the tube of the invention, the vulcanized elastomer of the inner layer is chosen from the components EPDM (polyolefin elastomer), nitrile polyvinyl chloride (PVC), and chlorosulfonated polyethylene (CSM).
The outer layer is chosen from the polyamides such as PA6, PA66, PA12. The outer polyamide can advantageously be filled with glass fiber.
Finally, the intermediate bonding layer is a substance based on ethylene, acrylic ester, and maleic anhydride.
In a second variant embodiment of the tube of the invention, the above-mentioned base structure, namely an elastomer layer, a thermoplastic layer, and a bonding layer, is covered by a vulcanized elastomer layer connected to the thermoplastic layer of the polyamide type via an intermediate bonding layer of the type described above.
The advantage of the coating lies mainly in the fact that the tube presents a flexible coating to the outside atmosphere, thereby damping noise and impacts and, by its vulcanized elastomer nature, possesses a structure that is cross-linked in three dimensions, thereby having the advantage of presenting quite good resistance to fire due to the fact that said structure does not collapse on itself under the effect of heat.